When trying to import the language, it seems to do something, just as when importing the whole SIL file but when double clicking the TSiLang component on the certain form we see nothing in the imported language

When importing the whole SIL file, we see the additional language as it should

Notice that in both cases we are working on a certain form, and not the whole project

I'm not sure if I understood properly: do you mean that only for ONE particular form the Load Language feature fails? Or it fails for any form from your project when you use Load language for selected form?